Composition and process for improving the adhesion of a metal to a polymeric material

ABSTRACT

The adhesion between a metal surface, e.g., a copper circuit trace, and a polymeric material, e.g., an epoxy insulator, is enhanced by treating the metal surface with a composition comprising:  
     A. Hydrogen peroxide,  
     B. An inorganic acid, e.g., a blend of sulfuric and phosphoric acids,  
     C. A corrosion inhibitor, e.g., a triazole,  
     D. A source of ammonium ion, e.g., ammonium phosphate, and  
     F. Water.  
     In a preferred embodiment, the treated metal surface is subsequently treated with a conditioner comprising:  
     A. Hydrogen peroxide,  
     B. An inorganic acid, e.g., sulfuric acid,  
     C. A corrosion inhibitor, e.g., a triazole,  
     D. An aromatic compound comprising a carboxlyic acid group, e.g., benzoic acid, and  
     E. Water.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/225,947 filed Aug. 17, 2000.

FIELD OF THE INVENTION

[0002] This invention relates to the manufacture of printed circuitboards (PCB). In one aspect, the invention relates to the manufacture ofmultilayer PCBs comprising alternating layers of metal circuits andinsulators while in another aspect, the invention relates to a processof adhering a metal circuit layer to an insulation layer. In yet anotheraspect, the invention relates to a composition useful in promoting theadhesion between a metal circuit layer and an insulation layer whilestill in another aspect, the invention relates to a composition andprocess for imparting a desirable color to the metal circuit layer.

BACKGROUND OF THE INVENTION

[0003] Multilayer PCBs and their various methods of manufacture are wellknown in the art. Typically, a copper foil is laminated to a dielectricsubstrate, the copper foil masked in a circuit trace pattern, theunmasked copper foil is removed by chemical etching, the mask ischemically removed from the circuit trace, the copper surface of theunmasked circuit trace “roughened” with an adhesion-promotingcomposition and laminated to a polymeric insulator (e.g., an epoxy).Copper foil is then laminated to the insulator, and the process repeateduntil the desired PCB is complete.

[0004] The structural integrity of the PCB is dependent, at least inpart, on the adhesion between the individual layers of the laminate.Adhesion between a metal, e.g., copper, copper alloy, aluminum, etc.,circuit trace and a polymeric insulator has been the subject of muchstudy. Metal, particularly copper and copper alloys, is known to tarnishupon exposure to oxygen, and this tarnish is known to interfere with thebonding between the circuit trace and the insulator. Accordingly,well-established practice in the art is to chemically treat the metalcircuit trace to remove the tarnish and roughen the metal surface. Thisroughening provides an enhanced surface area to which the insulator canpenetrate into the metal when the finished stack is subjected to heatand pressure during the final stages of the PCB manufacturing process.

[0005] Many chemical treatments are known for promoting the adhesionbetween a metal circuit trace and a polymeric insulator. Thecompositions taught in U.S. Pat. Nos. 6,054,061, 6,036,658, 6,020,029,5,928,790, 5,869,130, 5,800,859, 5,578,341, 5,476,947 and 5,037,482 arerepresentative. The entire disclosure of each of these patents isincorporated herein by reference. While all of these compositions areeffective to one degree or another, the PCB manufacturing industry has acontinuing interest in new compositions and their methods of use thatpromote the adhesion between a metal circuit trace and a polymericinsulator.

SUMMARY OF THE INVENTION

[0006] In one embodiment of this invention, the adhesion between a metalsurface and a polymeric material is promoted by treating the metalsurface with a composition comprising:

[0007] A. Hydrogen peroxide,

[0008] B. An inorganic acid,

[0009] C. A corrosion inhibitor,

[0010] D. An ammonium ion, and

[0011] E. Water.

[0012] Typically, the inorganic acid comprises a combination of sulfuricand/or phosphoric acid, the corrosion inhibitor is a triazole, and thesource of the ammonium ion is an inorganic compound, e.g., ammoniumphosphate. The metal surface, typically a copper circuit trace, istreated with the composition of this invention in a conventional manner.

[0013] In another embodiment of this invention, subsequent to treatmentwith the adhesion-promoting composition described in the precedingparagraph, the metal surface is treated with a color-enhancingcomposition comprising:

[0014] A. Hydrogen peroxide,

[0015] B. An inorganic acid,

[0016] C. A corrosion inhibitor,

[0017] D. An aromatic compound comprising a carboxylic acid group and ora salt of a carboxylic acid group, and

[0018] E. Water.

[0019] Typically, the inorganic acid is sulfuric acid, the corrosioninhibitor is a triazole, and the aromatic compound comprising acarboxylic acid group is a benzoic acid. Treatment with this“conditioner” composition darkens the surface previously treated withthe adhesion-promoting composition to enhance its aesthetic appearanceand/or improve the ability to optically detect defects.

BRIEF DESCRIPTION OF THE FIGURES

[0020]FIG. 1 is a graph reporting the peel strength of variouscopper/polymeric insulator laminates in which the copper layer wastreated with one of three adhesion-promoting compounds.

[0021]FIG. 2 is a scanning electron micrograph of a copper surfacetreated with an adhesion-promoting composition of this invention.

[0022] FIGS. 3-5 are scanning electron micrographs of three separatecopper surfaces each treated with a different prior artadhesion-promoting composition.

DESCRIPTION OF THE PREFERRED EMOBIDMENT

[0023] The adhesion-promoting composition of this invention is anaqueous composition comprising hydrogen peroxide, one or more inorganicacids, a corrosion inhibitor and an ammonium ion (preferably derivedfrom an inorganic compound). While other ingredients can be present,e.g., surfactants, fragrances, stabilizers, coloring agents and thelike, preferably the adhesion-promoting compositions of this inventionconsist only of hydrogen peroxide, one or more inorganic acids, acorrosion inhibitor, ammonium ion and water.

[0024] Hydrogen peroxide, typically added in the form of a 50% by weightaqueous solution, is present in the adhesion-promoting composition in aconcentration of at least about 1, preferably at least about 2 and morepreferably at least about 3 percent by weight active hydrogen peroxide.The maximum amount of hydrogen peroxide in the composition of thisinvention can vary to convenience, but typically it does not exceedabout 10, preferably it does not exceed about 4 and more preferably itdoes not exceed about 3.5, percent by weight of the composition.

[0025] The inorganic acid component of the composition comprises one ormore inorganic acids, preferably a mixture of two or more organic acids,more preferably a mixture of phosphoric and sulfuric acid in a weightratio of 1 to 3 to 3 to 1. The sulfuric acid usually is added in theform of a 50% by weight aqueous solution, and the phosphoric acid isusually added in the form of an 85% by weight aqueous solution. Theinorganic acid is present in the adhesion-promoting composition in anamount of at least about 2, preferably at least about 20 and morepreferably at least about 35, percent by weight of the composition. Themaximum amount of inorganic acid in the composition of this inventioncan vary to convenience, but typically it is not in excess of 60,preferably not in excess of 50 and more preferably not in excess of 40,percent by weight of the composition.

[0026] In terms of the inorganic acid comprising a blend of sulfuric andphosphoric acid, typically the sulfuric acid is present in theadhesion-promoting composition in an amount of at least about 1,preferably at least about 10 and more preferably at least about 17,percent by weight, and the phosphoric acid is present in an amount of atleast about 1, preferably at least about 8 and more preferably at leastabout 10, percent by weight. The maximum amount of these components inthe composition of this invention can vary to convenience, but typicallythe sulfuric acid does not exceed about 40, preferably it does notexceed about 30 and more preferably it does not exceed about 20, percentby weight, and typically the phosphoric acid does not exceed about 20,preferably it does not exceed about 15 and more preferably it does notexceed about 12, percent by weight.

[0027] The corrosion inhibitor is typically a triazole, tetrazole orimidazole. The unsubstituted and substituted triazoles andbenzotriazoles are preferred. Typical substituents include C₁₋₄ alkylgroups. Benzotriazole is a preferred corrosion inhibitor.

[0028] The corrosion inhibitor is typically present in an amount of atleast 0.1, preferably at least about 0.3 and more preferably at leastabout 0.5, percent by weight of the composition. The maximum amount ofcorrosion inhibitor in the composition of this invention can vary toconvenience, but typically the corrosion inhibitor does not exceed about5, preferably it does not exceed about 3 and more preferably it does notexceed about 1, percent by weight of the composition.

[0029] Any source of ammonium ion that is compatible with the otheringredients of the adhesion-promoting composition of this invention canbe used to prepare the adhesion-promoting composition of this invention.Typically and preferably the ammonium-ion source is an inorganiccompound, e.g., ammonium phosphate or sulfate, more preferably aphosphate, with ammonium phosphate a particularly preferred source ofammonium ion.

[0030] The source of ammonium ion is present in the adhesion-promotingcomposition of the present invention typically in an amount of at leastabout 0.1, preferably at least about 0.5 and more preferably at leastabout 1, percent by weight of the composition. The maximum amount ofammonium ion source in the composition of this invention can vary toconvenience but typically does not exceed about 5, preferably it doesnot exceed about 4 and more preferably it does not exceed about 2,percent by weight of the composition.

[0031] Water, preferably of a purity exceeding 1 megaohm specificresistivity, comprises the balance of the adhesion-promotingcomposition.

[0032] The color-enhancing composition, also known as a conditioner, ofthe present invention is also an aqueous composition comprising hydrogenperoxide, an inorganic acid and a corrosion inhibitor. However, incontrast to the adhesion-promoting composition described above, theammonium ion is replaced with an aromatic compound containing acarboxylic acid/salt group. Like the adhesion-promoting composition, theconditioner can contain other ingredients such as a stabilizer for thehydrogen peroxide, a fragrance, a coloring agent, and the like (buttypically not a source of ammonium ion), although preferably theconditioner consists only of an aqueous solution of hydrogen peroxide,an inorganic acid, a corrosion inhibitor and an aromatic compound with acarboxylic acid group or a salt of a carboxylic group.

[0033] The hydrogen peroxide of the conditioner is present in an amountsimilar to that described above for the amount of hydrogen peroxidepresent in the adhesion-promoting composition. Likewise, the inorganicacid can be the same and used in the same amounts as that described forthe adhesion-promoting composition above. However, preferably theinorganic acid of the conditioner is sulfuric acid alone in an amount ofat least about 1, preferably at least about 10 and more preferably atleast about 12, percent by weight of the conditioner. The maximum amountof sulfuric acid typically does not exceed about 40, preferably it doesnot exceed about 30 and more preferably it does not exceed about 15,percent by weight of the conditioner.

[0034] The corrosion inhibitor of, and the amount of the inhibitor usedin, the conditioner is the same as the inhibitor and amount used in theadhesion-promoting composition. Again, preferably the corrosioninhibitor is benzotriazole present in an amount between about 0.1 andabout 5% by weight of the conditioner.

[0035] Any aromatic compound comprising a carboxylic acid or salt groupthat is compatible with the other ingredients of the conditioner can beused as the aromatic compound with a carboxylic acid group in theconditioner. The aromatic component, e.g., benzyl, indenyl, etc., of thecompound can comprise one or more substitutents in addition to the atleast one carboxylic group, e.g., an amine, but preferably isunsubstituted except for the at least one carboxylic acid group, e.g., agroup derived from formic, acetic or propionic acid. Representative suchcompounds include p-aminobenzoic acid, p-hydroxybenzoic acid, benzoicacid and their sodium and potassium salts. The aromatic compound withthe carboxylic acid group is typically present in an amount of at least0.1, preferably at least about 0.2 and more preferably at least about0.4, percent by weight of the conditioner. The maximum amount of thiscompound typically does not exceed about 5, preferably it does notexceed about 1 and more preferably does not exceed about 0.8, percent byweight of the conditioner.

[0036] Both the adhesion-promoting composition and the conditioner areprepared in a conventional manner. The individual components are mixedwith water, preferably deionized water, in accordance with standardmixing procedures. The hydrogen peroxide is typically added in dilutedform (as noted earlier, typically a 50% by weight solution) and afterall of the ingredients are combined, the resulting solution is wellagitated to form a homogeneous mix.

[0037] The adhesion-promoting composition of this invention is used inthe same manner as known adhesion-promoting compositions. After themetal surface, e.g., a copper or copper alloy surface, is cleaned bymechanical or chemical means, it is then contacted with theadhesion-promoter. The contact can be made by any conventional means,for example, immersion in a bath of the adhesion promotion composition,spraying the composition onto the metal surface, or any other means ofcontact. Typically, the contact is part of the continuous process and isconducted at a temperature between about 65 and 120 F. for a dwell timeof between about 20 seconds and 10 minutes (the exact dwell time afunction of, among other things, the contact temperature and theformulation of the adhesion-promoting composition). Use of theadhesion-promoting composition of this invention results in a roughenedmetal surface that provides substantial surface area, which in turnpromotes excellent adhesion with the polymeric insulator.

[0038] In one preferred embodiment of this invention, the roughenedmetal surface resulting from contact with the adhesion-promotingcomposition of this invention, is contacted with the conditioner of thisinvention. While some minimal amount of additional roughening to themetal surface may result from contact with the conditioner, the primarypurpose of the conditioner is to darken the color of the surfacepreviously treated with the adhesion-promoting composition. Thisdarkening of the surface color not only adds to the aesthetics of thePCB, but it also enhances the contrast between the surface and thecopper trace pattern and this, in turn, enhances the effectiveness of anoptical scan of the PCB for defects. The contact of the conditioner withthe roughened metal surface is conducted in the same manner as thecontact of the unroughened metal surface with the adhesion-promotingcomposition.

[0039] In a typical process using both the adhesion-promotingcomposition and the conditioner of this invention, a copper surface ispre-cleaned with an alkaline cleaner (or an acid cleaner depending uponthe copper surface condition) for a dwell time between about 1 and 5minutes at a temperature between about 100 and 120 F. The copper surfaceis then rinsed with deionized water, and then the copper surface isimmersed in the adhesion-promoting composition of the present inventionfor a dwell time of about 30-90 seconds at a temperature between about80-90 F. The copper surface is then removed from the bath of theadhesion-promoting composition, optionally rinsed with deionized water,and then immersed immediately into a bath of conditioner for a dwelltime about 30 to about 90 seconds at a temperature between about 80 andabout 100 F. The metal surface is then removed from the bath ofconditioner, again optionally rinsed with deionized water, and thenlaminated in conventional fashion with a polymeric insulator.

[0040] The embodiments of this invention are further described by thefollowing examples. Unless reported otherwise, all parts and percentagesare by weight.

SPECIFIC EMBODIMENTS

[0041] Preparation of the Adhesion-Promoting Composition

[0042] The adhesion-promoting composition used in these examplescomprised the following ingredients in weight percent based on theweight of the composition: Hydrogen Peroxide (50%) 5.0 Sulfuric Acid(50%) 17.6 Phosphoric Acid (85%) 10.0 Ammonium Phosphate Dibasic 1.03Benzotriazole 0.5 Water (purity >1 megaohm) 65.84

[0043] With continuous stirring and at ambient conditions, the acidswere added to the water followed by the ammonium phosphate dibasic,benzotriazole and hydrogen peroxide. The formulation was mixed untilclear (about 2-3 minutes).

[0044] Preparation of the Conditioner

[0045] The conditioner used in these examples comprised the followingingredients in weight percent based on the weight of the composition:Hydrogen Peroxide (50%) 2.1 Sulfuric Acid (50%) 12 p-Hydroxybenzoic Acid0.4 Benzotriazole 0.2 Water (purity >1 megaohm) 85.3

[0046] With continuous stirring and at ambient conditions, the acidswere added to the water followed by the benzotriazole and hydrogenperoxide. The formulation was mixed until clear (about 2-3 minutes).

[0047] Comparative Adhesion-Promoting Compositions

[0048] Two comparative adhesion-promoting compositions were prepared.The first imitated the formulation of U.S. Pat. No. 6,036,758, andcomprised the following ingredients in weight percent based on theweight of the composition: Hydrogen Peroxide (50%) 4.0 Sulfuric Acid(50%) 15.9 Benzotriazole 0.43 Sodium m-nitrobenzene sulfonate 0.05 Water(purity >1 megaohm) 78.37

[0049] The second imitated the formulation of U.S. Pat. No. 6,054,061,and comprised the following ingredients in weight percent based on theweight of the composition: Hydrogen Peroxide (50%) 2.8 Sulfuric Acid(50%) 13.9 Phosphoric Acid (85%) 4.2 Benzotriazole 0.68 TetramethylAmmonium Hydroxide (25%) 0.65 Water (purity >1 megaohm) 79.1

[0050] Both formulations were prepared in a manner similar to theadhesion-promoting formulation of the invention, i.e., with continuousstirring and at ambient conditions, the acids were added to the waterfollowed by the benzotriazole and sodium m-nitrobenzene sulfonate ortetramethyl ammonium hydroxide, respectively, and hydrogen peroxide. Theformulations were mixed until clear (about 2-3 minutes).

[0051] Treatment of Copper Surfaces

[0052] Copper coupons (2×2 inches) were sheared from a panel clad withor consisting entirely of copper foil in accordance with IPC MF150. Thecoupons were cleaned by immersion in a bath of water and alkalinecleaner (5% v/v). The alkaline cleaner comprised deionized water (42 wt%), monoethanolamime (35 wt %), a 25 wt % solution of tetramethylammonium hydroxide (9 wt %) and a 85 wt % solution of ethylene diamine(14 wt %). The bath was maintained at a temperature of 100 F., and thedwell time for the coupons in the bath was about 2 minutes.

[0053] Upon removal of the coupons from the bath, each were rinsed intap water for about 2 minutes, and then immersed in a bath of anadhesion-promoting composition. The bath was maintained at a temperatureof about 90 F., and the coupons remained immersed for about 1 minute.The coupons were then removed from the bath, and rinsed with tap water.For those coupons not subsequently treated with the conditioner, thecoupons were allowed to air dry and then subjected to electronmicroscopy. For those coupons that were subsequently treated with theconditioner, the coupons were immersed in a bath of conditionermaintained at 80 F. for about 1 minute, removed, rinsed with tap waterfor about 1 minute, allowed to air dry, and then subjected to electronmicroscopy.

[0054] The scanning electron micrographs reported in FIGS. 2-5 show thatthe copper surface treated with the adhesion-promoting composition ofthis invention (FIG. 2) has both deeper crevices, which in turn producea better bonding surface (e.g., more surface area) for lamination with apolymeric insulator, and a different, apparently less fragile, grainshape (or morphology) as compared to the metal surfaces formed bytreatment with the comparative adhesion-promoting compositions(Comparative Composition from Example 104 of U.S. Pat. No. 6,054,061 inFIG. 3; Comparative Composition from Example 2 of U.S. Pat. No.6,036,758 in FIG. 4 and Comparative Example from column 6 of U.S. Pat.No. 6,020,029 in FIG. 5). The micrographs are reported at 3,000magnification.

[0055] Peel Strength

[0056] Identical coupons were prepared in the manner described above,and then laminated to a rigid dielectric core by the protocol of IPC4101. These coupons were then subjected to the peel strength protocol ofIPC TM 650, sections 2.4.8 and 2.4.40. In the following tables, the peelstrength of these coupons are reported in pounds per linear inch. Someof the coupons were not treated with an adhesion-promoting composition,but rather were mechanically treated (i.e., scrubbed). Although not asstrong as the bond created by the black oxide treatment, the peelstrength of the laminates in which the copper metal was treated with theadhesion-promoting composition of this invention proved stronger thanthat of the laminates prepared with a copper metal treated with aconventional adhesion-promoting compound or mechanically treated. TABLEI Peel Strength (lb/in) of a Laminate Prepared from a Metal SurfaceTreated with an Adhesion-Promoting Composition and a Polymeric MaterialAdhesion- Elevated Promoting AS IS¹ Post-Float² Temperature³ CompositionPanel Panel (F) A 4.6 4.36 4.22 B 6.53 6.15 7.63 C 3.43 N.D. N.D.

[0057] TABLE II Peel Strength (lb/in) of a Laminate Prepared from aMetal Surface Treated to Promote Adhesion with a Polymeric Material, anda Polymeric Material Adhesion-Promoting Average Minimum MaximumComposition or Bond Bond Bond Technique Strength Strength Strength A 4.12.6 5.8 B 1.1 0.8 1.6 C 0.4 0 0.8

[0058] The data in Table I is presented graphically in FIG. 1. Asreported in FIG. 1, laminates prepared from a metal surface treated withthe inventive composition have stronger peel strength than thoselaminates prepared from a metal treated with a comparative compositionin both short and long dwell time scenarios. While the black oxidetechnique provides a stronger peel strength in short dwell timescenarios, the inventive composition provides faster processing speed,reduced processing steps and lower operational costs than the blackoxide technique.

[0059] Although the invention has been described above in considerabledetail, both narratively and by way of example, this detail is for thepurpose of illustration, and it is not to be construed as a limitationon the scope of the invention as described in the appended claims.

What is claimed is:
 1. An adhesion-promoting composition comprising: A.Hydrogen peroxide, B. An inorganic acid, C. A corrosion inhibitor, D. Anammonium ion, and E. Water.
 2. An adhesion-promoting compositioncomprising, in weight percent based upon the weight of the composition,about: A. 1-10% hydrogen peroxide, B. 1-60% inorganic acid, C. 0.1-5%corrosion inhibitor, D. 0.1-5% of an ammonium ion source, and E. Water3. The composition of claim 2 in which the inorganic acid is a blend ofsulfuric and phosphoric acid at a molar ratio between about 3:1 and 1:3.4. The composition of claim 3 in which the corrosion inhibitor isbenzotriazole.
 5. The composition of claim 4 in which the source ofammonium ion is ammonium phosphate.
 6. A conditioner for a roughenedmetal surface, the conditioner comprising: A. Hydrogen peroxide, B. Aninorganic acid, C. A corrosion inhibitor, D. An aromatic compoundcomprising a carboxylic acid group, and E. Water.
 7. A conditioner fortreating a roughened metal surface, the conditioner comprising, inweight percent based upon the weight of the conditioner, about: A. 1-10%hydrogen peroxide, B. 1-40% inorganic acid, C. 0.1-5% corrosioninhibitor, D. 0.1-5% of an aromatic compound comprising a carboxylicacid group, and E. Water.
 8. The conditioner of claim 7 in which theinorganic acid is sulfuric acid.
 9. The conditioner of claim 8 in whichthe corrosion inhibitor is benzotriazole.
 10. The conditioner of claim 9in which the aromatic compound is at least one of p-aminobenzoic acid,p-hydroxybenzoic acid and benzoic acid.
 11. A system for promoting theadhesion of a metal surface to a polymeric material, the systemcomprising: (i) a composition comprising: A. Hydrogen peroxide, B. Aninorganic acid, C. A corrosion inhibitor, D. An ammonium ion, and E.Water; and (ii) a conditioner comprising: A. Hydrogen peroxide, B. Aninorganic acid, C. A corrosion inhibitor, D. An aromatic compoundcomprising a carboxylic acid group, and E. Water.
 12. A copper metaltreated with the composition of claim
 1. 13. A roughened copper metaltreated with the conditioner of claim
 6. 14. A copper metal firsttreated with a composition comprising: A. Hydrogen peroxide, B. Aninorganic acid, C. A corrosion inhibitor, D. An ammonium ion, and E.Water; and, subsequently treated with a conditioner comprising: A.Hydrogen peroxide, B. An inorganic acid, C. A corrosion inhibitor, D. Anaromatic compound comprising a carboxylic acid group, and E. Water. 15.A process for treating a metal surface, the process comprising the stepof contacting the metal surface with the composition of claim
 1. 16. Aprocess of treating a metal surface, the process comprising the step oftreating the metal surface with the conditioner of claim
 6. 17. Aprocess of treating a metal surface, the process comprising the steps offirst treating the metal surface with a composition comprising: A.Hydrogen peroxide, B. An inorganic acid, C. A corrosion inhibitor, D. Anammonium ion, and E. Water; and, then treating the metal surface with aconditioner comprising: A. Hydrogen peroxide, B. An inorganic acid, C. Acorrosion inhibitor, D. An aromatic compound comprising a carboxylicacid group, and E. Water.